The present invention relates to a process for making wet-layed fibrous, nonwoven webs or sheets. In particular, the present invention relates to such webs comprised of metal or refractory fibers, with nylon as a binder.
Papers comprised primarily of metal or refractory fibers have been desired by the industry for many years. Various methods have been developed for the preparation of metal fiber sheets. The manufacture of metal fiber nonwoven fabric-like paper structures on papermaking equipment has also been actively pursued due to its commercial attractiveness. Interest in such techniques is described, for example, in the chapter on metal fibers by Hanns F. Arledter in Synthetic Fibers in Papermaking, Editor O. Battista, chapter 6, pages 118-184. See also U.S. Pat. No. 2,971,877.
The problem in making metal fiber webs or sheets using conventional papermaking techniques is that the metal fibers tend to clump together. This can also be true for refractory fibers, particularly when the fibers are of some length, e.g., greater than xc2xd inch. Before paper can be made, it is necessary to open fiber bundles to achieve individual fibers and to disperse the fibers uniformly in a fluid. With most wood pulps, the opening is not usually a difficult task. The pulp or source of fibers is placed in water and the mixture is sheared until the bundles open.
With metal and refractory fibers, both the opening of the bundles and the dispersion of the fibers in order to keep the fibers separated are difficult. Normal types of mixing or shearing devices can easily damage metal and refractory fibers. When metal fibers are bent, they will remain bent and eventually will interact to form balls of tangled fibers. Refractory fibers also tend to tangle. Paper made from fibers in this form is unacceptable.
In addition to an improved process, an appropriate binder for metal and refractory fibers is also an important issue. The binder stabilizes the non-woven web and provides strength. The same binders useful for cellulose fibers may not be as useful for metal or refractory fibers. Therefore, use of an appropriate binder can improve metal fiber or refractory fiber sheets for particular applications, or in general, while continuing to use conventional processing.
It would therefore be of great interest to the industry to improve sheets of metal fibers and for refractory fibers by using an improved binder therefor.
It would also be of great advantage to the industry if a process for making a metal or refractory fiber sheet using conventional papermaking techniques, i.e., a wet-laying technique, was available. Such a process should offer efficiency and commercial viability particularly in terms of cost and performance. A combination of an improved binder with such a process would be highly valued.
Accordingly, it is an object of the present invention to provide a non-woven metal or refractory fiber sheet with nylon as the binder.
Yet another object of the present inventions to provide a process for making a wet-layed metal fiber nonwoven sheet which is efficient and effective.
These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto.
In accordance with the foregoing objectives, provided by the present invention is a nonwoven fiber web which employs nylon as the binder. The web is preferably comprised of metal or refractory fibers, for which the nylon binder has been found to work extremely well with metal fibers and refractory fibers such as carbon fibers. As a binder, it provides excellent strength and a very suitable melting point for applications in which the metal fiber sheets or refractory fiber sheets would be used.
In another embodiment, the present invention provides a process for making a wet-layed, metal fiber or refractory fiber nonwoven web. The process comprises forming a foam furnish by agitating metal fibers or refractory fibers in a foamed medium with an apparatus comprising agitating means mounted for displacement within the foamed medium and including a leading surface facing in the direction of displacement. The leading surface comprises upper and lower portions converging in the direction of displacement to form a generally convex leading surface. Preferably, the agitating means includes a non convex trailing surface facing away the direction of displacement, the surface being generally concave. The apparatus used in agitating the fibers also comprises driving means for displacing the agitating means in the direction of displacement for dispersing and mutually separating the fibers within the foamed medium. The foam furnish is then passed onto a screen and defoamed to form the nonwoven fibrous web.
Among other factors, the present invention is at least partly based upon the recognition that nylon is a uniquely applicable binder for metal fibers or refractory fibers such as carbon. The use of nylon permits one to form strong, nonwoven webs of metal fibers or refractory fibers, which have applicability in harsh environments. Furthermore, employing the process of the present invention one can form extremely uniform webs of the metal fibers and refractory fibers, with the nylon binders being employed and binding the fiber structures at the interstices.